A newly discovered star is so big, bright and strange that its appearance may be pointing us towards a cluster of dark matter in the sky.

Called Mothra by its discoverers, this star appears strangely bright in the sky during the 10.4 billion years it took to reach us. According to a team led by astrophysicist José Diego of the Spanish National Research Council in Spain, this places it in the extremely rare class of "kaiju" stars: distant monster stars with abnormally large apparent brightness.

One more star in this category has been detected and is significantly brighter than Mothra. This star, named Godzilla, was also discovered by Diego and his colleagues and has been described as the brightest known star in the sky.

Despite their differences, these two stars have some intriguing similarities, suggesting that massive dark matter smudges lurk in the space between them and us.

Diego and his team say this could be a probe that places constraints on dark matter, which in turn could help us narrow down what dark matter actually is.

Mothra, more formally known as EMO J041608.8-240358, was discovered in observations of distant galaxies collected by the James Webb Space Telescope. Even JWST, no matter how powerful it is, often has difficulty picking out individual stars over such vast gulfs of space and time, but this region of space is one that is strongly magnified by a gravitational lens.

They occur due to the curvature of spacetime around a large object in space, such as a galaxy or galaxy cluster. Any light travelling through this curved spacetime can be distorted, multiplied and magnified. This peculiarity of the cosmos, predicted by Einstein's general theory of relativity, allows us to see more distant objects in much greater detail than their distance would normally allow.

Both Godzilla and Mothra are in parts of space twisted by the clusters of galaxies between us and them. This provides some magnification, making the stars appear brighter. They were bright objects to begin with.

The researchers combed through archival data from the Hubble Space Telescope and found two observations taken six months apart in 2014 that captured the star.

By combining this data with JWST data, the team was able to calculate the star's properties. According to Diego and his colleagues' calculations, Mothra is probably a binary of two supergiant stars, one red and one blue.

The red star is cooler and dimmer, about 5,000 Kelvin and 50,000 Suns bright. The blue star is much hotter, at 14,000 Kelvin and a brightness of about 125,000 Suns.

But it's the magnification that's interesting. The galaxy cluster alone cannot explain Mothra's magnification, which the team found to be at least 4,000 times. There is something closer to the star that gives it an additional magnification.

Playing with the numbers a bit more, the team found that whatever this thing is, it's between 10,000 and 2.5 million times the mass of the Sun, the size of a dwarf galaxy or star cluster. But we can't see it; it doesn't show up in JWST or Hubble observations.

The team says this suggests that the object could be a dwarf galaxy composed almost entirely of dark matter. Such an object is not unprecedented. Dark matter is the invisible glue of the Universe, and most galaxies have more dark matter than normal matter. And scientists have often detected objects that appear to be made of this mysterious material.

But the potential detection of the Godzilla and Mothra dark matter spots suggests that they may be relatively common in the Universe. And lensing could be a tool we can use to find them. This could help to place constraints on dark matter.

"The existence of these millennia is fully consistent with expectations from the standard cold dark matter model," Diego and colleagues write. "On the other hand, the presence of such a small substructure in a cluster environment has implications for other dark matter models."

For example, it rules out the existence of hot dark matter and axion dark matter - the other two theories - outside a certain mass range. Future discoveries of kaiju stars could help narrow this field even further.

Perhaps the smoking gun of dark matter will be a triple star system called Ghidorah.

 

Source: https://www.sciencealert.com/